Alternating current rectifier



April 29, 1952 ALTERNATING Filed Sepb. l5, 1948 F. E'. SMITH CURRENTRECTIFIER 8 Sheets-Sheet l REDUCED VOLTAGE SYNCHRONOUS SELECTO RSYNCHRONOUS MCTOP.

PLUS

INDucTloN zscn PIER D C. LOAD INVENTOR. FaQ/wf ./f. 6W/7H April 29, 1952F. E. SMITH I ALTERNATING CURRENT RECTIFIER 8 Sheets-Sheet 2 Filed Sept.15, 1948 INVENTOR. FFAA/K 5717/777/ TOP/Vf y April 29, 1952 F. E. sMn-H2,594,594

ALTERNATING CURRENT RECTIFIER Filed Sept. 15, 1948 8 Shees--Slfleel'l 3F. E. SMITH ALTERNATING CURRENT RECTIFIER April 29, 1952 8 Sheets-Sheet4 Filed Sept. l5, 1948 April 29, 1952 F. E. SMITH 2,594,594

ALTERNATING CURRENT RECTIFIER Filed sept. 15, 194s 8 Sheets-Sheet 5 Ti7.. E.

April 29, 1952 `F, E, SMITH 2,594,594

ALTERNATING CURRENT RECTIFIER Filed Sept. l5, 1948 8 Sheets-Sheet 6INVENTOR. I /fP/eW/f ./f. 5/7/76/ RQZL April 29, 1952 F. E. sMl'rH2,594,594

ALTERNATING CURRENT RECTIFIER Filed Sept. l5, 1948 8 Sheets-Sheet 7Tij-. LE.

INVENTOR. fkw/ VA/ T 577/77/ April 29, 1952 F. E. SMITH 2,594,594

ALTERNATING CURRENT RECTIFIER Filed Sept. l5, 1948 8 Sheets-Sheet 8 TAPS FO R RE D U C E D VOLTAG E Z/ f5 SELECTOR Z057 5/? lZ /ZZf PLUS aINDucTloN RECTIFIER Y? Z/,

26 :L lE. .C. F LOA D INVENTOR. /CPQ/v/f 5/*7/77/ Patented pr. 29, 1952UNITED STATES PATENT OFFICE ALTERNATING CURRENT RECTIFIER Frank E.Smith, Niagara Falls, N. Y. Application September 15, 1948, Serial No.49,333 28 Claims. (Cl. 321-50) This invention relates to a system forconverting alternating current to direct current. It also relates to asynchronous selector for separating the alternating currents whichproceed in one direction from those which proceed in the oppositedirection, directing them into the load lines of a D. C. system. It alsorelates to induction rectiers. It also relates to switches, particularlyto rotary switches. It also relates to synchronous selectors employingsodium switches. It relates to a system of supplying molten sodium toelectric systems employing it and includes circuit breaking sodiumfeeders. It includes an A. C. D. C. system, a portion of which is sealedand operated in an atmosphere of nitrogen or of other inert gas. Theinvention also involves a number of dependent but important conceptswhich will be more fully set forth hereinafter.

Most current supply is of alternating current type. Nevertheless, thereare large demands in industry for direct current. The most satisfactorymanner of supplying this demand is to convert A. C. to D. C., and anumber of converters working upon different principles have beenconstructed to accomplish the conversion. There are rotary A. C.-D. C.converters, vacuum tubes, mercury arc and copper oxide converters, aswell asv those of a mechanical switch type wherein an attempt is made byswitches to direct the crests of the alternating current sine waves intoone D. C. line and the nodes into another, the load being connectedbetween the two lines. The use of mechanical switch apparatus toaccomplish this result has been tried in monophase circuits but has beenaccompanied by such great Vdifficulties that there has been nodevelopment along those lines in comparison to very great development inthe other types.

Polyphase circuits and systems are most widely used for the distributionof electric power. It is helpful in thinking of polyphase circuits tokeep in mind that any system having more than one circuit is a polyphasesystem, and that each phase may be considered as a separate current orcircuit. Because of their method of generation, polyphase alternatingcurrents can be represented on a graph by a number of sine wavescorresponding to the number of phases, the several waves being separatedand, in effect, following each other across the graph. The portion ofeach wave above the zero line of the graph is considered to be currentproceeding in one direction and that portion of the wave below the zeroline is considered to be current proceeding in the other direction. Theobject of converting systems is to rectify this current so that isproceeds only in one direction. Alternating current systems of two totwelve or more phases have been made and more or less successfullyoperated, and it is to be understood that the several principles o fthis invention are applicable to all such systems. However, thecommonest of all systems being three phase A. C., this invention will beparticularly described with respect to the converting of that type ofcurrent to D. C.

The several prior art types of converter have all been subject to severehandicaps and to material limitations in their eiliciency and theircapacity. For example, some of them produce a fluctuating D. C. currentwhich is less than satisfactory for general use and which has a seriousproblem in making the D. C. current flow, because the A. C. potential isemployed to make the D. C. current flow and the current in a succeedingphase will no't fiow until the E. M. F. in the preceding phase hasfallen below its own E. M. F. This results in a vertual stoppage ofcurrent, as one phase relinquishes and the succeeding phase takes over.A particular difliculty with prior art rectifying systems lay inachieving full use of the potential of the polyphase A. C. circuit.Ingeneral,.little use has been made of the negative potential of suchcircuits. Another diflicultywith the prior art rectifier systems hasbeen expressed as a poor power factor. Still another difficulty hasarisen by reason of short circuits from the high to the low potentialplus phases when the load on or resistance of the line varies so thatthe current may short between the high and low plus phases.

In the mechanical switch type of rectifier, of which there are very few,there has been great objection because of the tendency of the switchpoints to arc and burn out or at least to deposit upon the face of one,metal drawn fromA the body of the other and thus to make imperfect theclosing of the points. Sometimes these points when subjected to anoverload will burn out, requiring the rebuilding of the apparatus.

A particular need of any rectifying system is that it shall satisfy therequirements of full'and varying degrees of load, with efficiency.

It is an object of this invention to make a rectifying system, operableat substantial unity power factor, which is an improvement over theprior art in at least one and preferably in many or all the respectshereinabove noted. In particular, it is an object of the invention toconstruct a rectifying system in which the ilow of current in asucceeding phase will bis initiated before the potential of that phaseexceeds the potential of the preceding phase.

Another` object of the invention is to employ the full positive andnegative potential of a polyphase circuit, and especially to employ thefull negative potential thereof.

Another object of the invention is to reduce or to eliminate thepossibility of short circuits from one phase of high potential to anadjacent phase of like sign and of low potential.

Yet another object of the invention is to make a synchronous selectorhaving superior switching gear in which the making and breakingr ofcontacts is accomplished without destruction or wear of the contacts,and which are consequently capable of remaining in use for longerperiodsof time than has heretofore been possible.

Another object of the invention is to reduce the magnitude of thefluctuations in theE. M. F. of the D. C. system produced by conversionof Y A. C. current.

In the preferred form of the invention, the system includes a. deltatype transformer. In a modified form of the invention a Y type polyphasetransformer is employed. The two systems. have material differences, thelatter requiring fewer parts but the delta type being of superiorefficiency.

In the accompanying drawings,

Fig. 1 is a diagrammatic view of a delta-connected, three-phase A. C.D.C. rectifying system including asynchronous selector and an inductionrectifier in both the plus and minus D. C. lines.

Fig. Zisa side view largely in elevation, otherwise in section, of asynchronous selector.

Fig.- 3 is a section on the line 3-3 of Fig. 2.

Fig. 4 is a vertical section through an induction rectifier.

Fig. 5 is a section on the line 5 5 of Fig. 4.

Fig. 6 is an enlarged section through one turn of the winding of Fig. 4.

Fig. 7- is a vertical sectional view ofthe circuit breaking sodiumfeeder, taken on line 'F.- of Fig. 8.

Fig. 8 is an elevational view of the said feeder;

Fig. 9 is a section on line 9-5 of Fig. 3.

Fig. 10 is a diagram of the disksv showing conductor placement for thecorrect relation of three-phase current.

Figcll is a section on linelG--Iii of Fig. 3.

Fig. 12 is a section through the modified form of synchronous selectoremployed in the form of the invention of Fig. 13.

Fig.' 13 is a diagrammatic view of a. modied form of the inventionemploying a Y type transformer.

Fig. 14 isan enlarged elevation of the winding of the rectifier.

In Fig. 1 the numeral II indicates a threephase A. C. transformersecondary which is supplied with current by a primary P, constructed inany usual manner. The letters A, B, and C indicate the three phases andthe three phase lines that issue from the ldelta connected windingsA offthe transformer secondary. Between thesephase lines A. B and'C and therespective.

usv

4 windings of the transformer are taps such as I2`, I3, I4 and I5 of theA phase, which may be selectively connected to reduce the Voltage of thephases and to give the apparatus a flexibility it would not otherwisepossess. The three phase lines are connected to different connections ofa synchronous selector I5 within which the current is rectied and fromwhich it issues on one side by lines I?, I8, I9 as plus D. C. and fromthe opposite side of which, by means of lines 20, 2I, 22, it 'enters asrerectied A. C. Between the D. C. load and the synchronizing timer, onboth the positive and negative sides of the load, are inductionrectiiers 23, 23, the function of which in the system is important.

The function of the several parts of the invention will be betterunderstood after a consideration has been had of their novel structure.

Referring first to Figs. 2 and 3, A, B, and C indicate the phase linesdiagrammatically shown in Fig. 1 as they are connected Ato thesynchronous selector. These lines are electrically connected as shown insectional detail in Fig. 3 to a metal tube 2li which is held in aflexible insulator 25 that is in turn sealed in a boss 26 provided witha conical seat 2 conforming to a like conical seat on the insulator. Theinsulator is provided with a ledge 28 upon which rests a washer 29 whichis penetrated by bolts 30. Any degree of sealing pressure can beapplied'to the insulator 25.by means of washer 23. As afurtherprotection against the entry or escape ofv gases to or from the sealedcasing I5 of the synchronous selector, a packing gland 3l may beprovided in the end of the insulator. The tube 2li is connected at itsouter end to a tube 32= through which molten sodium is carried from acircuit breaker feeder 33.

Molten sodium is a good conductor, but it must be maintained attemperature in order to remain molten. Consequently, the line 32includes two other concentriclines 34, 35, of which tube 34 has a sealedend, and 35 an open end which terminates short of the end of tube 34.The hot oil is forced through the pipe 35 into the tube 34 and thecasing I6 to a position adjacent to a major double contact or sodiumswitch point 35, the detailed construction of which is shown in Fig. 11,which should now be examined.

Carried byv the tube 24 and thev insulator through which it passes is across head tube 3l fromwhich two slidable hollow sleeves 38 project. Thebores 33' within these sleeves extend to a positionV adjacent theenlarged contact heads 39 which have flat faces 4I) in which are formedannular grooves 4l which are connected by small passages 42 with thebore 38. The face 4I! of the Contact member 38 is a contact face throughwhich the current entering through the tube 2li, and themolten sodiumthatit contains is transmitted to the metal contacts i3 in the rotors ofthe synchronous selector.

Themolten sodium makes its way through the channels provided in theparts first described to the grooves in the faces ofthe contacts andforms spring 46. betweenv the two' contacts 3.8 urges them.

outward and into contact with the rotors. A facing of insulation 41 isprovided for the contacts 38 and this serves to clean the approachingface of the rotor, to prevent excessive wear of the leading edge of thecontact, and to prevent drawing out a spark. The contacts 38 may be ofmetal or they may equally well be made of ceramic or some non-conductingmaterial inasmuch as sodium will itself transmit the current. However,metal is preferred.

In Fig. 3 the contacts are not provided with the several grooves of Fig.but with a single cup 40' which receives the sodium from the bore 36 ofthe contact.

There are many advantages inherent in the novel construction which hasjust been described. The molten sodium forms a nlm between rotor and xedcontact and reduces Wear. If an arc is drawn out between a rotating anda fixed contact, the sodium lm between the faceswill vaporize andprotect the contacts and the apparatus against damage. In rotaryswitches having solid metal to solid metal contact, the iiow of currentcauses pockets to form in one member and accumulations of metal to beacquired by the corresponding contact, necessitating repairs andreplacement of parts, and shortening the use of the machine. By virtueof the new conceptions involving conducting liquid film contacts thelife of the contacts is greatly increased, and the period of use of themachine without halt for repairs is greatly extended.

A shaft '50 is rotatably mounted in bearings 52 and passes throughpacking glands 5I into the casing. It is screw threaded at 53, 53 forthe reception of nuts 54 which serve to position annular grips 55, 56,51. Grip 56 has an annular web 56' projecting centrally from a sleeve 56and carries an internally bevelled double flange 56". The grip 5'5 hasan annular web 55 projecting from a sleeve 55" and carries a singleinwardly bevelled ange 55". Grip 51 is like grip 55. The sleeves of thegrips are received over, and sleeve 56" is keyed to the shaft 50, sothat they rotate with the shaft in assembled position. The grip 55 andgrip '56 hold between them a rotor 59 which has a hub 60 with outwardlybevelled faces 6I corresponding to the bevels of the grips. Theconstruction of rotor 62 is like that of rotor 59 and is similarlymounted between grips 56 and 51. By adjusting the nuts 54 the positionof the rotors may be precisely adjusted along the shaft 5U. A pluralityof copper conductors 63 extend through the rotors from side to side. Inthe form of the invention being described there are five of theseconductors shown in Fig. 9, equally spaced on each rotor and containedwithin arcs of l18 degrees. The rotors are so positioned on the shaftthat the plus and minus discs connect their respective phasesalternately.

The contacts A+, A- are aligned with A; contacts B+, B- with B; and C+,C.- with C. The conductors are numbered 63 and the 63'.

- The rotors 56 and 62 are identical except in the angular position oftheir contacts with respect to each other. They are conveniently made ofglass or ceramic material, for instance, porcelain. They are preferablyground and polished after being positioned on the shaft so that thelateral faces will rotate in a true plane and furnish a minimum offrictional resistance to the xed contacts.

The shaft 50 is driven through a 5 to 1 reduction gearing 6.4 which isin turn driven by a synchronous'motor 65 which takes its power. from thesecondary that supplies the system. It must be understood that thisdescription applies to the form of the invention which is beingparticularly described but that different gear ratios could be employedwith other polyphase systems and other numbers of contacts on the discs.

As the motor is driven, current is fed through phase lines A, B and C tothe three double contacts 31 between the discs. In the position shown inFig. 3 the conductor 63 is connecting the contact 31 with anothercontact 66 which enters through the side wall. At that moment the Aphase is delivering positive current to the line, and that current istransmitted through sodium contact 31, conductor 63, and contact 66, themolten sodium furnishing a perfect make andv break at each place. As thepositive potential in phase A approaches zero, the contact 63 moves awayfrom contacts 31 and 66 While a-contact in disc '59 approaches contacts31 and 61. lAs the current reverses in phase A, becoming negative,contact is broken by contact 53 of the disc -62 and contact is madebetween 31 and 61 by a copper contact disc '59 so that phase A isconnected through contact 61 and not through contact 66.

Inasmuch as a synchronous motor is employed to drive the discs, thismake and break can be accomplished with precision. The stators of the'synchronous motor can be rotated a little in aclvance or in retard toachieve with precision any timing desired.

The conductor and contacts should be within- 1A cycle to remove thedanger of the center conv The discs may be rotated at 720 R. P. M. forsixty cycle threei tact snorting 63 and 63'.

phase current and at 300 R. P. M. cycle three phase current. occurs in72 degrees. The contact brushes of each sign (-1- or will accordingly`be located at 96 degrees from each other, since B phase is 1A; cycleadvanced over A, as C is over B;

From each side of the casing I6 there issue three contacts, the threenegative contacts being given the numbers 61, 68, 69 andthe three pluscontacts, the numbers 10, 1I, 12. The construction of these contactswith their brushes is signilar to the construction of 25, differing inthat there is no T-shaped member 36, the brush 13 extending directlyoutward from the tube 14 which is set in the insulator 15. The contacts61, 68 and 69 are connected to negative D. C. current for twenty-fivelines 22, 2I and 20 while contacts 10, 1I, and 12 are connected topositive D. C. phase lines I 3, I6, I1. Each of the phases delivers itspositive current in sequence to its own phase line, and the phase lines20, 2I, 22 receive the negative D. C. current in sequence. y

At this point it is noted that the lines I1, I8, I9 could be directlyattached to a bus bar, and the lines 20, 2I, 22 could be directlyattached to another bus bar, the two bus bars serving to supply D. C.current to a load. So far as is known that has been theproposal of priorattempts to rectify current by mechanical switching. However, suchsystems are faulty" in their operation under different conditions. Forinstance, if the circuit is suddenly opened so that there is no loadwhile'phase A has high positive potentialy and phase B very low positivepotential, a short may occur from phase A to phase B to the internaldestruction of the wiring of the system. Other difculties arise in suchsystems because of the relatively pulsating nature of the currentdelivered,` there being a very considerable difference One completecyclev afb/91455914.

7 between .the E. E at the crest :of one phase vaandsthe E. .F `ofthatfpha'se at the moinentrwhen the :succeeding ,phase takes zover.Gonsequently, .I .have incorporated in my :system novel conceptions:calculated to produce fa more even flow of D. C. current, to reduce fortotally eliminate the possibility ofshortlcircuits through the .several'l- :gand phases, and to .deliver `power with a :minimumof loss.Consequently, .in -combination with. the A:synchronous selector, thereis included in -my preferred system a new apparatus.. called eninduction rectifier. The .induction rectiers .are themselves novel. onthe -plusside .may be :used in -one .formbut the preferred formof1theinventionincludes a 'recti- `fier on the, negative :side also..An-induction rectiler .as employed in this specication :and the claimsYis Va vcircuit employing the magnetic :field created 'by the currentflowing -in -fone phase 'to resist counter-'now lof current in otherphases wound with-it. Whenso functioning it permits flow inone:direction only. Y

Referring .-nowlto .Figs-4, .14, 5 and 6, thenumorals IB, A8, ll'l Iarethe +A phase, B phase and C .phaselines respectivelyof the rectifiedcurrent. These svires are enclosed in insulation 80,.so they are.protected against short lcircuiting to each other. These wires are laidin parallel and are wound withinaflat steel'wire 8l whichi slaid in onedirection andagain in a yiiat `.steel wire 82 which .isiaidinrthe otherdirection. These three phase wires are thus encabled in a metall-icVcasing -of -good `flux -conducting properties, the wire constitutionv:being Dr'tcularly VVchosen with that .property in mind.4 The cable,whichis given .the generic .number v.83, is wound about a core -84 which4may be a permanent magnet, or simply of soft .iron or of Ymagneticsteel. Ther `core 84 shouldhave goodiiux Yconducting properties. Itscharacteristics .can be changed by selection of materialsfor ,particularrates of discharge. It is joined atits .ends by yokes 86, 86' to posts81, 8.8.

Wedges 8'9 support .the windings of the core 83 Within vthe posts 81,"88. whichare, vin section, more orfless .triangular with curved sides.

The .current that flows .through thelines .I-I. I 8 and 1l`9 directcurrent. Consequently, as `.each of '.'these .lines .receives the.discharge of :its connected phase, a -circular .iiux .about the linelis established, varying .in intensity. The steel.

windings .81., B2 ...invite Vthat .ux not only. to travel Lin ,its owndirection ybut to vinclude in .its circuit all three phase lines..Consequently-'the .flux about the .cableis the ,sum of .the.-u-Xesexisting .aboutthe individual .wiresand lacks theivariation in.intensity which is lcharacteristic of,` :the ux about. .a .single wire.The `coil -83 consequently acts as asingle Winding and energizes `the-core 8.4, establishing :a flow of nux, such Vas indicated by thearrows, which -is continuous xand -oiers substantially vno .resistance.and occasions substantiallynoiloss. :In all Vstandard systems, fdue to.their .lvoltagevdifferentiala only one. phase 'carries lthe Tl current:and `one .thenegative current. This :means th-atene phase mustcarry thefull maximum current, andthat .there :is a shock when one phasecomesvonand the iother letsgo. .That iniiuences .power factor tas -it 4throws`current yand potential 4outvof .step land contributes lto harmonicswhich :are fdisturbing to telephone zand :radio transmission. .'-Inparticular, if there is -a low power factor .in the supply current, the:current ow -fbecomes upset, :cuttingoff one .phase at tia very fhigh l.@and lcutting in aanother fat :za low :value :It ievenimeansiat timesthat there -`is yA :single rectifier no current iilowin'g. 4In Ithisinvention, on 'the other fhand, 'the :stored energy .in the core of theinduction rectifier supplied by -onegphase is transierred to thesucceeding phase so that .current startstoflow .in it vbeforeitstopszowing inthe rst ipha'se. Furthermore, the induction storesenergy in the core Which resists anycounterflow in :the -fcoil.

The induction .rectifier .is 'air-,cooled in small units and can beoil-cooled lwithin a casing in.v large units. The steel employed in therectifier may 'desirably :lie between the best silicon transformersteeland permanent magnetic steel. The choice will vary with loadconditions. The -unit permits .aiow resistance flow inonedirection aandimposes :high `resistance in the opposite direction. There are `twowindings so `closely associated Vthat mutual .indue-tance Ipreventsshort circuits. 'ihere vis helpful mutual .inductance between thecurrent carrying lines within the coil.

The three windings l1, I8, t9 are connected lto a ibus Ibar .-Qrl fromvwhich the load .92 drawsits current, andthe load-isconnected throughbus bar QZ `to .negative lines 20., .2 I, v22 `in whichis'anotherinduction rectier. The use of two induction rectiers, one in the Y-iandone in the .negative line, iis .a necessary feature vof the .inventionemploying .a .delta .connection and the :full and maximum E. lili. F. ofthe hfCnsupply.

In order to .maintain the system .employing sodium at .its Ahighestefficiency, the portions where sodium appears are prefer-ably sealedinanatmosphere of inert gas of `which:nitrogen is exemplary. Before beingadmitted to the system the nitrogen .is cleaned of all traces of gasescapable .of :reacting with `the sodium. The molten sodium being aconductor and being .fed inslow-ly moving streams to the variousbrushes, would carry the `current yto undesirable places .were it notfor the employment .of vcircuit breaking feeders of novel construction.The method .of maintaining zthe sodium .in a molten condition is alsonovel. In order .-to maintain all parts'of the apparatus `in'satisfactory running condition, which iis neither het enough Yto cause4excessive wear tin or damage to the system, :nor so -cold tha-t itcongeals the sodium, .-a :heating system Iis provided :Which'employs hotoiltor relatively iixed parts and streams :of heated nitrogen whereverneeded fior Amoving parts. These several portions of the inventionwillnow be described.

Referring again to Fig. 2 and .3., 'it is to be considered that the.casing i8 Vhas a sump 4100 which ygathers the vmolten sodium whichescapes from the brushes and returns "it through a pipe line ll to aWell |62 which -involves a container H13 :in Awhich `molten sodium isAmaintained at fa level lull. A tube extends downward .beneath the.level of the sodium and :a screen .ID-6 is lattached thereto and ltersthe sodium which is drawn from the well by a pump :I'lll .driven :bymotor 108. The sodium is forced by the pump through pipe line 4 09 to a.manifold ILI- which extends above lthe circuit .breaking sodiumvfeeders. .This manifold has aiweir Illl which maintains the sodium inVthe manifold ata level, the excess .sodium Abeing returned through pipei12 to vthe Asump in casing .16. The manifold lli! eXA tends alongside`the several .feeders one and ka portion fof `another of `which are.shown .inFig 7 at 1120, and .are connected thereto 'by vchannels 122|.The levelof the Vsodium in the manifold lill is above the bottom of thechannel I2I so that vthe sodium .iiows inward from r.the .manifold fto a`cup LZ2-inthe head 12.3fof the zfe'eder. Inith'e bottom of this cup isa needle valve seat |24 with which a needle valve stem |25 cooperates,being adjustable by means of a set screw |25 operable from outside thefeeder. This permits the sodium to fall in drops |21 down to the bottomof the feeder where it gathersin a pool 28 and passes through apassageway |29 into the sodium supply pipe 32 which is connected at itsother end to one of the brushes, for instance, to 24 as shown in Fig. 2.The supply pipe 32 is sealed at its end by packing gland-|30 throughwhich pass the oil supply pipes 34, 35. These concentric hot oil feedpipes extend to the positions shown in Fig. 3 so that the sodium ismaintained at proper temperature throughout the length of the pipes. Itis to be understood that in all cases where heat is applied insulationmay be employed, but the showing fof such insulation is omitted in orderto maintain the drawings in as simple a condition as is consistent withan adequate disclosure. The oil is circulated through dielectricdelivery pipes indicated in Fig. 2 at 34 and 35', in which system thereis a pump |3| which maintains sufficient circulation in the oil, and asteam oil heater |32 inthe same circuit maintains the oil attemperature. Circuit breaking feeders deliver sodium to each of the D.C. brushes, circuit breaking feeders deliver sodium to each of the D. C.brushes, and circuit breaker feeders serve each of the A. C. brushes ofthe synchronous selector. Hot oil pipe 34 heats the casing.

The circuit breakers may be of single wall construction but in cases oflarge electrical capacity are preferably of double wall construction,each wall |53, |54 being a glass or other dielectric cylinder clampedbetween the head |23 and a dielectric base member |55. Clamps |51 bearagainst an offset annulus |58 and against the bottom of the base member|55 in which the sodium orifice |29 is found. The inner cylindrical faceof the member |56 is tapered at |59, forming a tapered fit with thetapered bottom ofthe tube |54. The head |23 is attached to an insulatingring |60 by offset rods IBI, I 52, the spacing of such rods being suchthat adequate insulating distance is maintained between them. The ringhas nutsmolded in it, in which screw threaded rods are received to holdthe parts together.

In order to exclude oxygen from the system, it it maintained in anatmosphere of nitrogen under super atmospheric pressure. The nitrogen isdrawn from supply |40 through a tube |4| which extends downward beneaththe level of the sodium in the well |02, bubbling up through the sodium,in which all traces of undesired gas are removed, and passes out fromabove the surface of the sodium through a pipe |42 to the casing I6,from whence it passes by a pipe line |43 to a blower |44 and a steamheater |45 by which itis raised to a temperature sufficient to keepsodium molten. From the heater it passes by pipe line |46 to a pluralityof lines |41 to nozzles |48 which'are directed to the faces of the discs59, 52 andmaintain them at a temperature which prevents the congealingof the sodium. A nitrogen line |49 extends from the nitrogen heater orone of its lines to a position above the sodium feeders and is connectedthereto by pipes |50 as shown in Fig. 2 and Fig. 7. A small hole |5| inthe feeder admits nitrogen from tube |50 to the interior of the breakerfrom whence it is enabled to escape in a minor amount through smallorifices |52. From the orifices |52 the nitrogen is exhausted frombetween the two glasses |53,

10 l 54 forming the wall of the feeder and out through the opening |55.The size of the orifices |52 and |55 may be small enough to make theloss of nitrogen negligible and the construction of return linesunnecessary.

There is discussedhereinafter a modification of the invention in whichit is employed with a, Y- type transformer. This is illustrated in Figs.13 and l2. Although this modification appears to be simpler, it is notpreferred. Referring now to Figs. 13 and 12, the numeral 200 indicates aY- type transformer secondary having a neutral wire 20| and A, B, Cleads 202, 203, and 204, respectively, taps 205 being provided to alterthe Voltage of each phase. The phase leads are admitted to synchronousselector 206 on one side by sodium carrying tubes 201, 208, 209 whichare constructed and have sodium brushes 2|0 similar to those which havehereinbefore been described. A single rotary disc 2| is mounted on thesynchronously driven shaft 2|2, which is provided with transverseconductors 2 I3. Opposite brushes 2|4, 2|5, 2 I 6 are provided todeliver current through leads 2|?, 2|8, 2|9 to an induction rectifier220. From the induction rectifier the leads pass to a plus bar 226 andto a D. C. load, the return line 22| being connected to the neutral wire20| of the transformer secondary.

This modification shows the adaptability of the invention to othersystems than that of the preferred form, but it is noted that to attainan evenness of D. C. current comparable to that of the preferred form,the modification ought to have many more phases, for instance, twelve.Consequently, although this modification of the invention is simplier intheory it is inferior in some uses, particularly in those uses where D.C. current with small variation in E. M. F. is desired.

An advantage of this invention is in the construction of an A. C.-D. C.rectifier or converter system which is superior to the known systemsincluding the copper oxide rectifiers, the mercury arc rectifiers, andto monophase mechanical switching arrangements of the sort heretoforeattempted.

The combination with a polyphase system of synchronous selector andinduction -rectifiers marks a material advance in the construction ofconversion systems. The synchronous selector as described with itssodium contacts is adapted to precise construction and to long,continuous operation without halt for repairs. Almost the entireconstruction of this synchronous selector is new, including the switchesper se and the brushes. conductor is novel and has material electricaland mechanical advantages. The protection of the sodium from reactivegases is simple and satisfactory, and the means of delivering it to thepoint of use, convenient.

The induction rectifier protects the system against shorts andmalfunctioning of the circuits and improves the emciency ofrectification. The construction of the apparatus is simple in comparisonwith the results accomplished.

One of the notable electrical advances of the present invention isthattwo phases of the A. C. may deliver power simultaneously to the D.C. lines whereas in previous systems the delivery of one terminated asthe delivery of the next began. This overlap constitutes a materialadvance in the art.

In certain places the term polyphase D. C. is used, and although it isunusual, signifies a direct The method of employing sodium as aV ilcurrent substantiallyuniform in floW-andE. M. F. supplied Aby apolyphase A. C. system in which the full E. M. F. of the A. C'. systemis directed to produce the E. M.'F. of the D. C. load line.

Where D. C. phase wires is referred to, it' signiyplied with directcurrent by said synchronous selectonandan induction rectifier in saidload line YVbetween the load and the synchronous selector.

2. An electrical conversion apparatus includving a polyphasetransformer, a synchronous sellectorsupplied With polyphasealternating-current by said transformer, a load line supplied withpolyphase direct current by said synchronous selector, and inductionrectiers in said load line between the load and the synchronousselector, said synchronous selector including a casing, a `shaftextending into said casing, a pair of dielectric rotors on said shaft,each rotor having 'five transverse conductors offset from those of theother rotor, A. C. contacts between said :rotors aligned with the pathsof said transverse vconductors and connected to the phases of said ftransformenconduits extending to the contact faces lof said contacts,`means to deliver molten :sodium through said conduits to said contactfaces, D. C. contacts aligned with the A. C. rconritacts and withthepaths of said-transverse conn ductors on the outsides of said rotors,conduits extending to the contact vfaces of said D. C. contacts, ,meansto deliver molten sodium through said Aconduits to said D. C. contactfaces, circuit Abreakers in each sodium line, and means to drive saidrotors at one fth full A. C. generatorspeed comprising asynchronousmotor and reduction gearing.

3. An electrical conversion apparatus including a polyphase transformer,a synchronous selflectorsupplied with polyphase alternating cur-Vrent-.by said transformer; a load line supplied with polyphase directcurrent by said synchro- ,nous selector, and induction rectiers in saidvloadline between the load andthe synchronous selector, said synchronousselector including a casing, a shaft extending into said casing, a pairof dielectric rotors on said shaft, each rotor having five Vtransverseconductors offset from those of the other rotor, A. C. contacts betweensaid rotors aligned with the paths of said transverse conductors andconnected to the phases of said transformer, conduits extending to thecontact faces of 'said contacts, means to deliver a liquid 'conductorthrough said conduits to said contact faces, D. C. contacts aligned'with the A. C. contacts and with the paths of the said transverse'conductors' on the Voutside of said rotors, conduits extending to thecontact faces of said D. C. contacts, means to deliver a liquidconductor 'through said conduits to said D. C. contact faces, andmeansto drive said rotors at one fth full A. C. generator speedcomprising a synchronous ing a polyphase transformer, a synchronousselectorsupplied with polyphase alternatingjcurrent by `saidtransformer, a load Aline supplied with polyphase direct current by saidsynchronous selector, and induction rectifers in said load line betweenthe load and the synchronous selector, said synchronous selectorincluding a casing, a shaft in said'casing, a pair of Adielectric rotorson said shaft, each rotor having five -transverse conductors `offsetfrom those of the 5. An electric conversion apparatus includingA vapolyphase transformer, a synchronous selector supplied with polyphasealternating current .by said transformer, a load line supplied Withpolyphase D. C. by said synchronous selector, and induction rectifiersin said'load line between the load and the synchronous selector, saidsynchronous selectorincluding a casing, a shaftin said casing, a pair of.dielectric rotors Vonsaid. shaft, each rotor having transverseconductors offset from those of the other'rotor, A. C. contacts betweensaid rotors aligned `with the paths of said transverse conductors andconnected Vto the phases of the said transformer, conduits extending tothe contact 'faces of `said A. C. contacts, D. C. contacts on theoutsides of .said rotors aligned with the said A. C. contacts and withthe paths of said transverse conductors, conduits extending to thecontact faces of said D. C. contacts, means to deliver a .liquidconductor through said conduits to said contact faces, and vmeans todrive said rotor contacts in 'synchronism with the phase changes inthe'transformen 6. An electrical conversion apparatus including apolyphase transformer, asynchronous selector supplied With polyphasealternating current by said transformer, a load line supplied withpolyphaseV D. C. by said synchronous selector, and'induction rectifiersin said load line between the load and the synchronous selector, Asaidsynchronous selector including a casing, a

shaft in said casing, dielectric rotors on said shaft, each rotor havingtransverse conductors oifset from those of the other rotors, A. C.contacts on the paths of the transverse conductors onone side of eachrotor and connected to the phases of said transformer, conduitsextending to the contact faces of said A. C. contacts, D. C. contactsaligned with the A. C. contacts on the other side of said rotors,conduits extending to the contact faces of said D. C. contacts, means todeliver a liquid conductor through said conduits -to said contact faces,and means'to drive said rotor contacts in synchronismfvvith 'the .phasechanges in the transformer. I

7. An electrical conversion apparatus including a polyphase transformer,a synchronous selector supplied with polyphase alternating current bysaid transformer, a load line supplied with polyphase direct current bysaid synchronous selector, and induction rectiers in said load -linebetween the load and the synchronous selector, said synchronous selectorincluding a casing, a shaftin said casing, rotors on said shaft -havingalternating transverse conductors, A. C.

contacts on the paths of the transverse conductors on one side of eachrotor and connected to the phases'of said transformer, conduitsextendtending to the contact faces of said D. C. contacts, means todeliver a liquid conductor through saidl conduits to said contact faces,and means to drive said rotor contacts in synchronism with the phasechanges in the transformer.

8. An electrical conversion apparatus including a polyphase transformer,a synchronous selector supplied with polyphase alternating current bysaid transformer, a load line supplied with polyphase direct current bysaid synchronous selector, and induction rectiers in said load linebetween the load and the synchronous selector, said synchronous selectorincluding separate contacts connected to the several phases of thetransformer, a pair of space conductors aligned with each of saidcontacts, rotary conductor means constructed and arranged to makecontact alternately between each said separate contact and the contactsof its associated pair, means to maintain a nlm of liquid sodium betweensaid rotary conductor means and separate contacts, and means to engagethe rotary contact means with its associated pair of contactsalternately in synchronism with the change in direction of current flow.

9. An electrical conversion apparatus including a polyphase transformer,a synchronous selector supplied with polyphase alternating current bysaid transformer, a load line supplied with polyphase D. C. current bysaid synchronous selector, and induction rectiilers in said load linebetween the load and the synchronous selector, said synchronous selectorincluding separate contacts connected to the several phases of thetransformer, a pair of spaced contacts aligned with each of saidcontacts, rotary conductor means making contact alternately betweeneach` of said separate contacts and the the contacts of its associatedpair, means to maintain a film of liquid conductor between said rotaryconductor means and separate contacts, and means to engage the rotaryconductor means with its associated pair of contacts alternately insynchronism with the change in current direction in the transformer.

10. An electrical conversion apparatus including a source ofpolyphase A.C. current, a synchronous selector supplied with polyphase A. C. by saidsource, a plurality of lines supplied with D. C. from the A. C. phasesof said source by said synchronous selector, and an induction rectifier'in said plurality of lines.

11. An electrical conversion apparatus including a source of polyphaseA. C. current, a synchronous selector supplied with polyphasealternating current by said source, a load line supplied with polyphasedirect current by saidsynchronous selector, and induction reetilers insaid load line between the load and the syn.- chronous selector,including a figure-eight core of transformer core metal the center bar owhich carries a winding composed of the insulated D. C. phase wires laidin parallel and enclosed in a flexible metal case of high permeancewithin an oil cooled metal housing.

12. An electrical conversion apparatus including a source of polyphaseA. C. current, a synchronous selector supplied with polyphase alterla lvnating current by said source, a load line sup-'- plied with polyphasedirect current by said synchronous selector, and induction rectifiers insaid load line between the load and the synchronous selector, includinga. figure-eight core of transformer core metal the center bar `of whichcarries a winding composed of the insulated D. C. phase wires laid inparallel and enclosed in a flexible metal case of high permeanee.

13. An electrical conversion apparatus including a source of polyphaseA. C. current, a synchronous selector supplied with polyphasealternating current by said source, a load line supplied with polyphaseD. C. current by said synchronous selector, and induction rectifiers insaid load line between the load and the synchronous selector, includinga looped core of high permeance metal, one part of which carries awinding composed oi the insulated D. C. phase Wires laid in parallel andenclosed in a flexible metal case of high permeance.

14. An electrical conversion apparatus including a source of polyphaseA. C. current, a synchronous selector supplied with polyphasealternating current by said source, a load line Vsupplied with polyphaseD. C. current by said synchronous selector, and induction rectiilers insaid load line between the load and the synchronous selector, includinga looped core of high permeance, one part of which carries a windingcomposed of a plurality of D. C. phase wires enclosed in a flexiblemetal case of high permeance.

15. An electrical conversion apparatus including a source of polyphaseA. C. current, a synchronous selector supplied with polyphasealterhating current by said source, a load line supplied with polyphaseD. C. current by said synchronous selector, and induction rectiers insaid load line between the load and the synchronous selector, includinga winding composed of a plurality of D. C. phase wires enclosed in aflexible metal case of high permeance and a closed flux conductor inmagnetic vassociation with said winding.

16. An electrical conversion apparatus including a source of polyphaseA. C. current, a synchronous selector supplied with polyphasealterhating current by said source, a load line supplied with polyphaseD. C. current by .said synchronous selector, and induction rectifiers insaid load line between the load and the synchronous selector, includinga winding composed of a plurality of insulated D. C. phase wires woundin parallel about a portion of a flux conducting loop.

17. An induction rectifier for three phase D. C. current including acore of high permeance having a winding composed of three parallel,insulated conductors for the phases, said insulated conductors beingcabled in a plurality of oppositely laid windings of flat metal stripsof high permeance and wound about the core, and a plurality of closedmetallic flux paths of high permeance looped about said winding.

.1.8. An induction rectifier including a core of high permeance having awinding composed of parallel insulated conductors for the phases, saidinsulated conductors being cabled in a plurality of oppositely laidwindings of ilat metal strips of high permeance and wound about thecore, and a plurality of closed metallic magnetic flux paths of highpermeance looped about said winding.

19. An induction rectifier including a core of high permeance having awinding composed of a plurality of separate conductors for the phases,

said conductors being cabled in a nexible casing of' high permeance,said cableY being wound about theicor'e, and a metallic flux path ofhigh. permeance connecting the ends of the core.

20. An induction rectiiier including a Winding composed of separateconductors for the phases enclosed in a flexible casing of highpermeance, and ux conducting means connecting the ends of the winding.

21'. An induction rectiiier including a winding composed of a pluralityof insulated conductors for the separate phases wound in a tight coilabout a portion of a magnetic nux ccnductin metallic loop. I

n22. A synchronous selector including contacts corresponding in numberto the number of phases of al .polyphase system, a pair of spacedcontacts aligned with each of said contacts, rotary conne'ctor'meansmaking contact alternately between eachof said phase contacts and thecontacts of its associated pair, means to maintain a nlm of liquidconductor between said contacts, and means to engage each rotary contactwith its associated pair o contacts alternately. Y

' 23. A synchronous selector including three aligned, spaced contacts,rotary conductors *between said contacts, said rotary conductors beingangularly spaced whereby to connect the centrali of the three contactsalternately with the other contacts, and means to maintain a film ofliquid. sodium between said contacts and conductors at engagement.

24. A synchronous selector including three aligned, spaced contacts,rotary conductors between said contacts, said rotary conductors beingangular-ly spaced whereby to connect the centralof the three contactsalternately with the other contacts, and conduit means to supply theface oione of said contacts with a liquid conductor.

25. In electrical apparatus a plurality ofv polyphasev current lines, asynchronous selector transmitting D. C. from said lines to an equalnumber of D. C. lines, an induction rectifying means including a loopcore for the passage of iiux having a part within a coil formed of theD. C. lines, and av single D. C. line connected to said D. C. linesbeyond the coil.

26. In electrical apparatus a plurality of lines carrying polyphasecurrent, a synchronous selector transmitting D. C. from said lines to anequal number or" D. C. lines, and an induction rectifying means in theD. C. lines having low resistance in the direction of flow and highresistance to counteriiow.

27. A synchronous selector employed in. the conversion of polyphasealternating current supply to a direct current use consisting` of meansto direct the plus current to a plus induction rectifier and receive theminus current from a minus induction rectiier, said means consisting oftwo rotating dielectric discs containing con ductors for closing thecircuit between contacts on opposite sides of said discs, one of saidAcon.- tacts being connected to one phase of the A. C. supply and theother contact beingconnected to the plus leads of the D. C. circuit forone disc. and the negative leads of the D. C. circuit for the otherdisc, said contacts to be supplied with a liquid 'metallic conductivemedium for closing the space between said contacts and said conductors,the number of said conductors being atleast one more' than the number ofphases inthe supply and so spaced and operating at such a speed that theconductors make and break contact with.L the contactors when the currentisv `at or. near zero, the two discs being in spaced relationshipto'veach other.

28. An induction rectiiier employed inthe conversion of polyphasealternating current supply to a direct current use consisting of meansenergized by the maximum current flow and. maximum M. F. which allows owin one direction with a small resistance and opposite flow with a highresistance, said means consisting of an iron core of high permeabilitywound with. three parallel windings of insulated conductors, saidconductors being connected on one side to the individual outletconductors of a synchronous selector and on the other side to the bus ofa D. C. circuit.

Y FRANK E. SMITH.'

REESRENSES CETED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS- Number Name Date 728,299 Rice May 19, 19031,185,419 Lyle May 30, 1916 1,234,099 Lendi July 17, 1917 1,457,902Gardeen June 5, 1923 1,567,761 'Slepian Dec. 29, 1925 1,969,093 PothAug. '7, 1934 2,155,990 Janetschlie Apr. 18, 1939 2,169,031 Slepian Aug.8., 1939 2,182,628 Janetschke Dec. 5, 1939 2,293,296. Jonas Aug.. 18',1942 2,351,036 Grant June 13, 1944

